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March 1998

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Subject:
From:
"Leslie O. Connally" <[log in to unmask]>
Reply To:
Leslie O. Connally
Date:
Tue, 3 Mar 1998 13:29:19 -0800
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text/plain
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Jack,

It has been my experience that the Laminate Suppliers tend to report Dk on the
high Side. We have found, that when applying our Classical Impedance model to
the Board build that the apparent Dk is lower than the Suppliers literature. We
verified this by measuring Dielectric Spacing and Line widths and Transposing
the model to back calculate the Dk. We nearly always found the Actual Dk lower.

Within some bounds the higher the resin content the lower the Dk, This is
because the Glass reinforcement has a Higher Dk. The composite somewhat follows
the "Rule of Mixtures".

We usually find the Epoxy Dk to be between 4.0 and 4.2.

I hope this is some help.

Les Connally
[log in to unmask]

>  From: "Olson, Jack C" <[log in to unmask]>, on 3/3/98 9:21 AM:
>  WARNING: this is a very unexciting question...
>
>  My software does some basic signal integrity analysis,
>  and I just noticed it defaults the dielectric constant for
>  regular FR4 to 4.7
>
>  I was under the impression that most FR4 is at 4.2-4.3
>  these days (more resin? thinner cores? can't remember...)
>
>  Even a brief response will be appreciated!
>                                                                  Jack
>
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